Industrial plant for recovering solids from liquids

ABSTRACT

Apparatus for the removal of solids from liquids and concentrating the solids through the use of strainers. Solidladen water or other liquid is passed through an automatic selfcleaning strainer wherein the strainer media is cleaned by clean water flowing in a reverse direction, relative to the flow of dirty water therethrough. The backwash water is passed through a low pressure rotating screen type strainer assembly where the solids are removed and the clean water returned to the outlet of the self-cleaning strainer. Accumulated solids are continuously removed from the surface of the screens and discharged outside of the strainer assembly.

United States Patent Kinney June 13, 1972 [54] INDUSTRIAL PLANT FOR2,253,692 8/1941 DeGrave ..2l0/392 RECOVERING SOLIDS FROM LIQUIDS3,089,325 5/1963 Robbins et al. ..210/333 X [72] Inventor: Selwyne P.Kinney, Carnegie, Pa. p i L Decesare [73] Assignee: S. P. KinneyEngineers, Inc., Carnegie, Pa. Attorney pamlelee Utzler & welsh [22]Filed: July 6, 1970 57 ABSTRACT [21] Appl. N -I 2, 80 Apparatus for theremoval of solids from liquids and concentrating the solids through theuse of strainers. Solid-laden [52] U s C] 210/122 210/297 210/392 wateror other liquid is passed through an automatic self- 210/396 cleaningstrainer wherein the strainer media is cleaned by [51] Int Cl B01 d50/00 clean water flowing in a reverse direction, relative to the flow[58] Fieid 333 402 of dirty water therethrough. The backwash water ispassed 6 through a low pressure rotating screen type strainer assemblywhere the solids are removed and the: clean water returned to 56]References Cited the outlet of the self-cleaning strainer. Accumulatedsolids are continuously removed from the surface of the screens andUNITED STATES PATENTS discharged outside of the strainer assembly.

1,051,160 1/1913 Robacher ..210/396 12 Claims,6DrawingFigures u 42 64 mo52 s4 0 5 O 92 '3' Il O 68 O 90 54 9s 98 INDUSTRIAL PLANT FOR RECOVERINGSOLIDS FROM LIQUIDS This invention relates to an industrial plant forremoving solids from liquids, and more particularly to a backwash liquidstrainer assembly for use in combination with an automatic self-cleaningrotating drum strainer.

Automatic self-cleaning strainers, especially drum type, are extensivelyused in industry for removing solid matter from liquids. Often timesthey are used for eliminating foreign substances carried in surfacewater, such as streams or rivers. Typically constructed, these drumstrainers include a generally cylindrical housing containing a rotatingdrum having straining media arranged in openings through the bodythereof. Dirty water enters the drum strainer through an inlet port andis diverted through the drum where the heavy solid matter is strainedfrom the water. The clean water is directed from within the drum to anoutlet port where it is discharged to be used as needed. As the drumstrainer rotates, each vertical column of strainer elements passesbetween a backwash chamber where clean water flows in reverse directionthrough that column of strainers to flush away accumulated solids fromthe outer surface of the strainers. The solid laden backwash water isthen discharged from the backwash chamber. The discharged backwash waterwas either dumped on the ground surface around the drum strainer or intosettling tanks, or directed back to the river or stream from where theoriginal water came. It many cases it is desirable to recover the solidsfrom the backwash water for reuse, and also to recover the solids insuch a manner that the clean backwash water may be reused. In othercases, the interest is in preventing water pollution and thus inremoving solids from the backwash water and discharging the clean waterinto the rivers or streams from where it originally came. The usualmethod of removing the solids from the backwash water, for whateverpurpose, is to discharge the backwash water into a settling tank whichis not a very efficient way of removing solids from liquids. Thisinvention makes possible the efficient removal of solids from backwashliquids. With the present invention, backwash liquid is discharged intoa reservoir tank at atmospheric pressure from which it is withdrawnthrough a low pressure type strainer. The clean liquid is dischargedfrom the strainer to be used as desired. There is also provided meansfor removing the solids from the surface of the screens and dischargingthe solids externally of the strainer. This arrangement imposes no backpressure on the backwash system, concentrates the solids, and recoversthe liquid that would otherwise be wasted. Furthermore, it eliminatesthe need for settling tanks and also permits return of clean water torivers or streams.

More particularly, I provide a plant for the processing of liquidshaving solids therein, preferably comprising: an automatic self-cleaningrotary strainer; a reservoir tank communicating with the backwash outletof the rotary strainer for receiving and storing backwash liquid untilit is ready to be strained. The tank supports a strainer which includesa liquid inlet communicating with the interior of the tank. For example,I provide a disc-shaped mesh wire strainer having screens supported onthe ends of an annular housing which housing is arranged on a hollowshaft coupled to a motor. Inlet pipes are arranged on the shaft betweenthe screens and communicate with the interior of the shaft. Alsoprovided is a suction means extending from the exterior of the reservoirtank to communicate with the liquid inlet of the strainer for drawingliquid from the tank through the strainer and for then discharging theclean liquid externally of the tank. In my preferred embodiment I show apump coupled through suitable piping communicating with one of theliquid inlet pipes of the mesh strainer, i.e., the liquid inlet pipeimmersed in the liquid during rotation of the strainer. The cleanbackwash water may be discharged from the pump to be used as desired. Inthe embodiment described herein I show the discharge of the pump coupledwith the clean water outlet line coming from the rotary strainer. I alsoprovide scraper blades for scraping the accumulated solid matter fromthe mesh screens onto chutes for discharge outside of the reservoirtank.

Other details and advantages of this invention will become apparent asthe following description of a present preferred embodiment thereofproceeds.

In the accompanying drawings, I have shown a present preferredembodiment of this invention in which:

FIG. 1 is a side elevation view of a backwash liquid strainer assemblycoupled with a rotating drum strainer, the combination embodying oneform of the present invention, and showing the discharge of the pump ofthe strainer assembly coupled to the line coming from the outlet of thedrum strainer;

FIG. 2 is a plan view of the combination shown in FIG. 1;

FIG. 3 is a view taken along the line 3-3 of FIG. 1 and enlarged tobetter show the details of construction of the reservoir tank andstrainer means forming part of the present invention;

FIG. 4 is a view taken along the line 4-4 of FIG. 3 showing furtherdetails of construction of certain of the elements forming part of thepresent invention;

FIG. 5 is a view taken along the line 5-5 of FIG. 1 showing some detailsof construction of the elements of the rotating drum strainers; and

FIG. 6 is a plan view of a backwash liquid centrifuge solidliquidseparator assembly coupled with a rotating drum strainer, thecombination embodying another form of the present invention, and showingthe discharge of the pump of the separator assembly coupled to the linecoming from the outlet ofthe drum strainer.

Referring now to the drawings, there is shown a backwash liquid strainerassembly lo arranged with a high pressure, selfcleaning type rotatingdrum strainer 12. The drum strainer 12 is of any standard and well knowndesign and includes a generally cylindrical housing 14 having a dirtyliquid inlet 16 connected to a pipe 18 for transporting dirty water, forexample, from a stream, river or lake to the strainer. A clean liquidoutlet 20 is provided through housing 14 opposite to the inlet 16. Pipe22 is connected to outlet 20 and extends to a discharge opening,notshown, where the clean liquid passing therethrough is to be used. Abackwash liquid outlet 24is provided through housing 14 at right anglesto the inlet 16 and outlet 20. As shown in FIG. 5, a strainer drum 26 isarranged within housing 14 and is coupled with a motor 28, shown inFIGS. 1 and 2, for rotation about a vertical axis. There are numerousopenings through the drum 26 into which are fitted strainer elements 30.Dirty liquid entering housing 14 passes through the strainer elements 30and clean liquid is directed out of the housing 14 through outlet 20. Asthe drum 26 rotates, each vertical column of strainer elements30 passesbetween a generally vertically extending slot 35 behind which is abackwash chamber 34. Liquid flows in a reverse direction (relative todirty liquid flow) through the strainer elements 30 as they pass slot 35into the backwash chamber 34 to thereby flush away the accumulatedsolids on the strainer elements. The solid laden backwash water is thendischarged from the housing 14 through the backwash liquid outlet 24.All of the strainer elements 30 eventually pass across the backwashchamber 34 to be flushed clean.

The backwash liquid strainer assembly 10 includes an open top, foursided, generally rectangular cross-sectioned reservoir vessel or tank 40for storing solid laden backwash liquid until such time as the liquid isready to be strained. The reservoir tank 40 is connected to the backwashliquid outlet 24 of housing 14 through pipe 42 which is connected at oneend to a lower portion of tank 40 and at the other end to a handoperatedvalve 44 which in turn is connected to the backwash liquid outlet 24.

An open-ended hollow shaft member 50 is supported for rotation betweentwo side walls of reservoir tank 40. A wire mesh strainer means 51 isfixed to an intermediate portion of the shaft member 50, and includes anannular support housing 52 having radially extending support ribs 54fixed at the inner ends thereof to the shaft member 50 and flat supportwebs 56 arranged between pairs of ribs 54. Each of the webs 56 has acircular opening 57 through a mid-portion thereof; and extending fromeach opening 57 and fixed to each web 56 is a liquid inlet pipe 58, eachof which communicates with an opening 62 through shaft member 50. Thus,the liquid inlet pipes 58 communicate with the interior of shaft member50. Mesh wire screens are fixed to the open ends of annular housing 52,and surround portions of the shaft member 50. The size of the mesh ofscreens 64 is selected to preferably match that of the mesh of thestrainer elements of the drum 26 in the drum strainer 12. For example,if the strainer elements 30 have a 60 X 60 mesh, the screen 64 shouldlikewise have a 60 X 60 mesh. In addition, the surface area of screens64 should be preferably the same as the surface area of the strainerelements 30.

Each end portion of shaft member 50 extends beyond a side wall of thereservoir tank 40. A stub shaft 68 is force-fitted into the left endportion, as viewed in FIG. 4, of shaft member 50 and is secured to theshaft member as by welding between the stub shaft 68 and the end of theshaft member 50. Stub shaft 68 is supported for rotation at anintermediate portion thereof by bearing member 70 arranged on a groundsupported pedestal 71, and is coupled through a speed reducer 72 tomotor 74 which is connected with a source of electrical power,not shown.The right end portion of shaft member 50 is also supported for rotationby a bearing member 76.

A stationary hollow arbor is disposed within shaft member 50 and has oneend, the left end as viewed in FIG. 4, closed and the right end opened.An opening 82 extends radially through the arbor 80 to communicate withthe interior thereof. Arbor 80 is oriented within shaft member 50 sothat the axis of opening 82 is generally vertical and the opening 82faces the bottom of tank 40. Opening 82 is located near the left end ofthe arbor 80 such that the axis thereof will be in the vertical planeincluding the axes of the opening 62 through shaft member 50. Thus, whenshaft member 50 is rotated so that the axis on opening 62 is verticaland that opening 62 faces the bottom of tank 40, such opening 62 and theopening 82 through arbor 80 will be adjacent and coaxial, and a directpassage will exist between the confines of the tank 40 and the interiorof arbor 80. A spring biased seal 84 is arranged in opening 82 toprevent leakage of air from around the arbor 80 into opening 82 duringrotation of the strainer means when the interior of the arbor is underpump suction. Additional seals 86 and 88 are arranged between theinterior of shaft member 50 and the left and right end portions,respectively, of arbor 80, for also preventing air from entering thearbor 80. An end cap 90 surrounding a portion of arbor 80 is fixed onthe right end portion of shaft member 50 and serves to close the rightend ofthe shaft member.

The right end of arbor 80 is fixed to a check valve 92 for permittingthe liquid to flow only out of the arbor. The check valve 92 is coupledto a length of pipe 94 which, in turn, is coupled to the suction side ofa centrifugal pump 96 which is driven by a motor 98 connected to asource of electrical power, not shown. The pressure or discharge port ofthe pump 96 is connected with a pipe 100 which in turn is joined to pipe22 coming from the clean water outlet of the rotary drum strainer 12.Thus, the clean backwash water coming out of reservoir tank 40 willcombine with the clean water stream discharged from the rotating drumstrainer 12.

A pair of scraper units 102 is arranged in reservoir tank 40 forscraping the accumulated dewatered solid matter from the exterior of thescreens 64 and for discharging the solid matter for collection outsideof the tank. Each of the scraper blade units 102 includes a trough-likechute 104 arranged alongside a screen 64. Each chute 104 is cantileversupported by an end wall 40a of the reservoir tank 40, and is pitcheddownwardly from adjacent a point at an upper portion of the plane of ascreen 64 to a discharge end disposed outwardly of the end wall 40a.Thus, solid matter falling into a chute 104 will tend to travel down thechute to be discharged onto the ground outside of the reservoir tank 40.A scraper blade 106 is fixed to the upper edge of the inside wall ofeach chute 104, and is positioned to rub against the surface of a screen64, and thus scrape the accumulated solid from the screens as thestrainer means 51 is rotated through tank 40. The scraper blades 106 areinclined toward the chutes 104 to thereby facilitate the flow of thesolid waste into the chutes.

A float control 110 is supported by tank 40 at an upper portion thereoffor activating the drive motor 74 of the strainer means 51 and motor 98for pump 96 when the liquid in the tank 40 reaches a certain level. Thefloat control 110 includes a float member extending into the confines ofthe tank 40, which member is connected with a switch. The switch iselectrically connected to the motors 74 and 98. When the liquid in thetank 40 is below a certain level the switch is open and the motors arestopped; when the liquid in tank 40 reaches a certain level the floatmoves up to activate the switch and the motors start to thereby operatethe strainer means 51 and pump 96. Thus, solid laden backwash liquid isdrawn by pump 96 through the screens 64 to remove the solid matter, andthe clean liquid is discharged into the clean liquid stream coming fromthe drum strainer 12.

Depending on the industry in which drum type self-cleaning strainers areused, and the nature of the solids in the liquid, the volume of backwashliquid will generally be between I and 5 percent of the total capacityof the strainer. The strainer capacities range anywhere from 50 gallonsper minute to several thousand gallons per minute. This invention findsparticular application to installations in operations using the highercapacity strainers. Many thousands of gallons per day of backwash liquidare therefore to be dealt with, and at a backwash volume of 5 percentthe removable solids carried in 1,000 gallons of unstrained liquid areconcentrated in 50 gallons of backwash liquid and with a backwash ratioof 1 percent the removable solids are concentrated from 1,000 gallons to10 gallons. The high capacity high pressure drum type selfcleaningstrainers must be of heavy rugged construction designed for low pressuredrop, and would not be suitable for use in straining the relatively lowvolume of backwash liquid. On the other hand, rotating screen typestrainers, such as strainer assembly 10, are low volume, low velocity,and low pressure type strainers which would be entirely unsuited fordrum type strainer application, but which are eminently satisfactorystraining backwash liquid at low volumes and a high pressure drops.

FIG. 6 shows another embodiment of the present invention. In thisembodiment a low pressure centrifugal liquid-solid separator is used forseparating the solids from the liquids of the backwash liquid dischargedfrom the rotating drum strainer 12. The backwash liquid outlet 24 ofstrainer 12 is coupled to a reservoir vessel 132 through piping 134having a hand operating valve 136 therein. Piping 138 is coupled betweenvessel 132 and the hollow inlet pipe 140 of separator 130. Thecentrifugal separator 130 is shown more or less schematically since itrepresents any well-known separator, and, as such, forms no part of thepresent invention. Separator 130 is supported for rotation by a pair ofaxially arranged shafts 142 and 144, respectively, shaft 142 beinghollow and surrounding inlet pipe 140. A drive sheave 146 is shown fixedto shaft 140 which sheave is coupled to a drive motor 147. The inletpipe 140 extends to and communicates with the interior of centrifugalimpellar 150 which includes the usual continuous scroll-type blade 151.The impellar 150 is surrounded by a housing 152 having a sludgedischarge 154 at the left end thereof, as viewed in FIG. 6, and a cleanliquid discharge 156 at the right end thereof. The clean liquiddischarge 156 is coupled by piping 158 to the suction side of suctionpump 160. The discharge of pump 160, in turn, is coupled by piping 162to the outlet pipe 22 of drum strainer 12. Thus, the pump 160 drawsliquid from vessel 132 through inlet pipe 140, into the confines ofimpellar 150 out of openings 164, into engagement with blade 151 wherethe solids are separated from the liquid and the clean liquid is drawnthrough the pump 160 and discharged into outlet pipe 22. The solidsludge will be urged by the impellar blade 151 out of sludge discharge154. As in the earlier embodiment, the pump and separator motors may bearranged to begin operating simultaneously when the level of liquid invessel 132 reaches a prescribed point. Slmilarly, the motors will be setto stop when the level of liquid in vessel 132 drops below a certainpoint, not necessarily the same as the pump and separator startinglevel. The size of the separator 130 should be selected so that thedegree of separation of solids from the liquids passing therethrough isat least equivalent to the straining capacity of rotating drum strainer12. For example, if the strainer elements of strainer 12 are sized tostrain a certain size particle, then separator 130 should also be ableto separate that same size particle.

It should be apparent to those skilled in the art that various otherarrangements of the elements comprising the combination of thisinvention are possible. For example, the strainer means 51 can be madein various other forms well known in the strainer art; the scraper means102 may be substituted by a flush system, etc.

Iclaim:

l. A plant for processing of liquids having solids therein comprisingthe combination of:

an automatic self-cleaning strainer including a rotatable drum arrangedin a housing with a plurality of strainer elements disposed in openingsthrough the drum, liquid inlet means arranged to receive pressurizedliquid for directing the liquid to flow through such strainers, liquidoutlet means for receiving the strained pressurized liquid to dischargesame from the housing, backwash liquid means including a backwashchamber open to atmospheric pressure and a slot open to said strainerelements as they are rotated past the chamber whereby pressurized cleanliquid will flow through the strainer elements to force accumulatedsolid matter on the strainer elements into the backwash chamber, andbackwash liquid outlet means for receiving and discharging solid ladenbackwash liquid from said housing;

a backwash liquid strainer assembly comprising:

a reservoir tank communicating with the backwash liquid outlet means;

low pressure liquid-solid separating means including a liquid inletcommunicating with the interior of said tank, for separating the solidsfrom the liquids stored in said tank,

suction means extending from the exterior of said tank to saidseparating means for drawing liquid through said separating means anddischarging clean liquid externally of said tank; and

means for discharging solid sludge from said reservoir tank. I

2. The combination as set forth in claim 1 wherein said separating meansis a rotating drum strainer means supported by said tank and including aliquid inlet communicating with the interior of said tank for strainingliquid in the tank; and wherein said suction means extends from theexterior of said tank to the liquid inlet of said drum strainer meansfor drawing liquid from said tank through said strainer means anddischarging liquid externally of said tank.

3. The combination as set forth in claim 1 wherein said separating meansis a centrifuge means having an inlet communicating with the interior ofsaid tank; and wherein said suction means is coupled with the dischargeof said centrifuge means.

4. The combination as set forth in claim 2 wherein said suction meanscommunicates with the liquid outlet means of the rotating drum strainerfor discharging clean liquid into the liquid outlet means.

5 The combination as set forth in claim 2 including cleaning meanssupported by said tank for cleaning accumulated solid matter from saidstrainer means.

6. The combination as set forth in claim 2 wherein said strainer meansincludes a disc-shaped mesh strainer supported by said tank for rotationabout the axis thereof, and power means for driving said mesh strainer;and wherein the said suction means includes hollow piping extendingalong the axis of said mesh strainer. I

7. The combination as set forth in claim 6 wherein said suc' tion meansincludes a pump connected with said hollow piping, and drive means fordriving said pump; and including control means in said tank operativelyconnected with said power and drive means and responsive to the level ofliquid in said tank for operating said power and drive means when theliquid in said tank reaches a certain level.

8. A plant for processing of liquids having solids therein comprisingthe combination of:

an automatic self-cleaning strainer including a rotatable drum arrangedin a housing with a plurality of strainer elements disposed in openingsthrough the drum, liquid inlet means arranged to receive pressurizedliquid for directing the liquid to flow through said strainers, liquidoutlet means for receiving the strainer pressurized liquid to dischargesame from the housing, backwash liquid means including a backwashchamber open to atmospheric pressure and a slot open to said strainerelements as they are rotated past the chamber whereby pressurized cleanliquid will flow through the strainer elements to force accumulatedsolid matter on the strainer elements into the backwash chamber, andbackwash liquid outlet means for receiving and discharging solid ladenbackwash liquid from said housing;

a backwash liquid strainer assembly comprising:

a reservoir tank communicating with the backwash liquid outlet means;

disc-shaped mesh low pressure rotating drum strainer means supported bysaid tank for rotation about the axis thereof lying in a generallyhorizontal plane and sized such that a substantial portion thereof iswithin the confines of said tank;

said drum strainer means including a liquid inlet communicating with theinterior of said tank;

power means coupled with said drum strainer means for driving said drumstrainer means;

suction means extending from the exterior of said tank to said liquidinlet of said drum strainer for drawing liquid from said tank throughsaid drum strainer and discharging clean liquid externally of said tank;and

scraper means supported by said tank for scraping solid matter from saiddrum strainer and discharging same externally from said tank.

9. The combination as set forth in claim 8 wherein said drum strainermeans includes an elongated hollow shaft member extending across anintermediate portion of said tank; an open-ended annular support housingfixed to said shaft member; screen members fixed to the end peripheriesof said support housing; said liquid inlet of said drum strainer meansis arranged between said screen members and communicating with theinterior of said shaft: and wherein said suction means includes hollowpiping extending into said shaft member to communicate with said liquidinlet of said drum strainer means.

10. The combination as set forth in claim 9 wherein said liquid inlet ofsaid drum strainer means includes a plurality of arcuately spaced inletpipes extending radially from said shaft member and communicating withthe interior thereof; and including valve means in said hollow pipingfor opening said piping to one of said inlet pipes during rotation ofsaid shaft and admitting liquid into said piping.

11. The combination as set forth in claim 9 wherein said suction meansincludes a pump having inlet and discharge ports; drive means fordriving said pump; and including control means in said tank operativelyconnected with said power and drive means and responsive to the level ofliquid in said tank for operating said power and drive means when liquidin said tank reaches a certain level.

12. The combination as set forth in claim 11 including piping meanscoupling the discharge port of said pump to the liquid outlet means ofsaid self-cleaning strainer.

1. A plant for processing of liquids having solids therein comprisingthe combination of: an automatic self-cleaning strainer including arotatable drum arranged in a housing with a plurality of strainerelements disposed in openings through the drum, liquid inlet meansarranged to receive pressurized liquid for directing the liquid to flowthrough such strainers, liquid outlet means for receiving the strainedpressurized liquid to discharge same from the housing, backwash liquidmeans including a baCkwash chamber open to atmospheric pressure and aslot open to said strainer elements as they are rotated past the chamberwhereby pressurized clean liquid will flow through the strainer elementsto force accumulated solid matter on the strainer elements into thebackwash chamber, and backwash liquid outlet means for receiving anddischarging solid laden backwash liquid from said housing; a backwashliquid strainer assembly comprising: a reservoir tank communicating withthe backwash liquid outlet means; low pressure liquid-solid separatingmeans including a liquid inlet communicating with the interior of saidtank, for separating the solids from the liquids stored in said tank,suction means extending from the exterior of said tank to saidseparating means for drawing liquid through said separating means anddischarging clean liquid externally of said tank; and means fordischarging solid sludge from said reservoir tank.
 2. The combination asset forth in claim 1 wherein said separating means is a rotating drumstrainer means supported by said tank and including a liquid inletcommunicating with the interior of said tank for straining liquid in thetank; and wherein said suction means extends from the exterior of saidtank to the liquid inlet of said drum strainer means for drawing liquidfrom said tank through said strainer means and discharging liquidexternally of said tank.
 3. The combination as set forth in claim 1wherein said separating means is a centrifuge means having an inletcommunicating with the interior of said tank; and wherein said suctionmeans is coupled with the discharge of said centrifuge means.
 4. Thecombination as set forth in claim 2 wherein said suction meanscommunicates with the liquid outlet means of the rotating drum strainerfor discharging clean liquid into the liquid outlet means.
 5. Thecombination as set forth in claim 2 including cleaning means supportedby said tank for cleaning accumulated solid matter from said strainermeans.
 6. The combination as set forth in claim 2 wherein said strainermeans includes a disc-shaped mesh strainer supported by said tank forrotation about the axis thereof, and power means for driving said meshstrainer; and wherein the said suction means includes hollow pipingextending along the axis of said mesh strainer.
 7. The combination asset forth in claim 6 wherein said suction means includes a pumpconnected with said hollow piping, and drive means for driving saidpump; and including control means in said tank operatively connectedwith said power and drive means and responsive to the level of liquid insaid tank for operating said power and drive means when the liquid insaid tank reaches a certain level.
 8. A plant for processing of liquidshaving solids therein comprising the combination of: an automaticself-cleaning strainer including a rotatable drum arranged in a housingwith a plurality of strainer elements disposed in openings through thedrum, liquid inlet means arranged to receive pressurized liquid fordirecting the liquid to flow through said strainers, liquid outlet meansfor receiving the strainer pressurized liquid to discharge same from thehousing, backwash liquid means including a backwash chamber open toatmospheric pressure and a slot open to said strainer elements as theyare rotated past the chamber whereby pressurized clean liquid will flowthrough the strainer elements to force accumulated solid matter on thestrainer elements into the backwash chamber, and backwash liquid outletmeans for receiving and discharging solid laden backwash liquid fromsaid housing; a backwash liquid strainer assembly comprising: areservoir tank communicating with the backwash liquid outlet means;disc-shaped mesh low pressure rotating drum strainer means supported bysaid tank for rotation about the axis thereof lying in a generallyhorizontal plane and sized such that a substantial portion thereof iswithin the confines of said tank; said drum strainer means including aliquid inlet communicating with the interior of said tank; power meanscoupled with said drum strainer means for driving said drum strainermeans; suction means extending from the exterior of said tank to saidliquid inlet of said drum strainer for drawing liquid from said tankthrough said drum strainer and discharging clean liquid externally ofsaid tank; and scraper means supported by said tank for scraping solidmatter from said drum strainer and discharging same externally from saidtank.
 9. The combination as set forth in claim 8 wherein said drumstrainer means includes an elongated hollow shaft member extendingacross an intermediate portion of said tank; an open-ended annularsupport housing fixed to said shaft member; screen members fixed to theend peripheries of said support housing; said liquid inlet of said drumstrainer means is arranged between said screen members and communicatingwith the interior of said shaft: and wherein said suction means includeshollow piping extending into said shaft member to communicate with saidliquid inlet of said drum strainer means.
 10. The combination as setforth in claim 9 wherein said liquid inlet of said drum strainer meansincludes a plurality of arcuately spaced inlet pipes extending radiallyfrom said shaft member and communicating with the interior thereof; andincluding valve means in said hollow piping for opening said piping toone of said inlet pipes during rotation of said shaft and admittingliquid into said piping.
 11. The combination as set forth in claim 9wherein said suction means includes a pump having inlet and dischargeports; drive means for driving said pump; and including control means insaid tank operatively connected with said power and drive means andresponsive to the level of liquid in said tank for operating said powerand drive means when liquid in said tank reaches a certain level. 12.The combination as set forth in claim 11 including piping means couplingthe discharge port of said pump to the liquid outlet means of saidself-cleaning strainer.